133. Clone Graph

Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors.

OJ's undirected graph serialization:

Nodes are labeled uniquely.

We use # as a separator for each node, and , as a separator for node label and each neighbor of the node.

As an example, consider the serialized graph {0,1,2#1,2#2,2}.

The graph has a total of three nodes, and therefore contains three parts as separated by #.

1. First node is labeled as 0. Connect node 0 to both nodes 1 and 2.
2. Second node is labeled as 1. Connect node 1 to node 2.
3. Third node is labeled as 2. Connect node 2 to node 2 (itself), thus forming a self-cycle.

Visually, the graph looks like the following:

       1      / \     /   \    0 --- 2         / \         \_/

这是图的深度遍历，需要设置map来防止图的循环遍历，如果之前已经遍历过这个节点，返回map.get。代码如下：

/** * Definition for undirected graph. * class UndirectedGraphNode { *     int label; *     List<UndirectedGraphNode> neighbors; *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); } * }; */public class Solution {    private HashMap<Integer, UndirectedGraphNode> map = new HashMap<Integer, UndirectedGraphNode>();        public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {        if (node == null) {            return null;        }        if (map.containsKey(node.label)) {            return map.get(node.label);        }        UndirectedGraphNode clone = new UndirectedGraphNode(node.label);        map.put(clone.label, clone);        for (UndirectedGraphNode neighborNode: node.neighbors) {            clone.neighbors.add(cloneGraph(neighborNode));        }        return clone;    }}